Centrifugal clutch



0t 28, 1.947. l.. w. RAwsoN l 2,429,697 l CENTRIFUGAL CLUTCH Filed Jan.15, 1944 il Il! ou/s W. RAWSON www Patented oct. 2s, .19,47

CENTRIFUGAL CLUTCH Louis W. Rawson, Worcester, Mass., assignor toWorcester Polytechnic Institute, Worcester,

Mass., a corporation of Massachusetts Application January 15, 1944,Serial No. 518,430

4 Claims. 1

This invention relates to centrifugal clutches, and more particularly toclutches of the type having revoluble friction shoes which are thrownoutwardly by centrifugal force into Contact with a surrounding drum inorder that power may be transmitted from one rotatable element toanother.

Clutches of this type are often used in connection with internalcombustion engines to transmit power therefrom to other machines. Suchengines produce a pulsating torque, and the pulsations will traveldirectly through the usual clutch to the driven machine, causingvibration and yshortening the useful life of the machine. A reduction insuch vibration is highly desirable. It is also desirable to constructthe clutch in such a way that the shoes will remain out of engagementwith the drum until a predetermined speed is reached. This will permitthe engine to be started and to run at idling speed without transmittingany power. The clutch engaging speeds should be capable of accuratedetermination by comparatively simplecalculations.

It is accordingly one object of the invention to provide a relativelysimple and dependable centrifugal clutch particularly adapted forconnecting an internal combustion engine to a driven machine.

It is a further object of the invention to provide a centrifugal clutchwhich will serve not only as an eiiicient power-transmitting mechanismbut also as a means for damping torsional vibrations.

It is a further object of the invention to provide a centrifugal clutchwhich will operate efliciently throughout a long life of useful service,the construction being such that the speed required for clutchengagement can be readily calculated.

With these and other objects in view,l as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

Referring to the drawings illustrating one embodiment of the inventionand in which like reference numerals indicate like parts,

Fig. 1 is a longitudinal section through a centrifugal clutch, taken onthe line I--I of Fig. 2; Fig. 2 is asection on the line 2-2 of Fig. 1,the parts being shown in their stationary positions;

Fig. 3 is an enlarged view of a portion of Fig. 2, showing one of theclutch shoes in its engaged position;

Fig. 4 is a section through a clutch shoe, taken on the line 4--4 ofFig. 3;

Fig. 5 is a perspective view of a roller; and

Fig. 6 is a perspective View of a stop device.

The embodiment illustrated comprises a driving shaft I0 and a drivenshaft Il axially alignedV therewith. On the driving Ashaft I0 lthere ismounted a hub l2 having a hollow cylindrical portion I4 projectingcoaxially therefrom. The cylindrical portion I4 is providedwith a seriesof outwardly projecting radial ribs or abutments` l5 which are undercuton opposite sides to provide inwardly facing shoulders I6. These ribsform pockets therebetween for the reception of friction shoes I8, theribs having approximately radial plane surfaces I9 located outwardly 0fthe shoulders I6. A ring 20 is removably fastened by means of screws 2Ito the ribs I5 in order to close the ends of the pockets adjacent thehub I2, while permitting access to the shoes. On the driven shaft I Ithere is mounteda hub 23 which is connected by an outwardly extendingtransverse web 24 to a hollow cylindrical drum 25, This drum surroundsthe friction shoes I8. As the driving shaft I0 rotates, the ribs I5 willforce the shoes I8 to revolve, and centrifugal force will cause theshoes to move outwardly into frictional engagement with the innersurface of the drum 25 (if the speed is sufficiently high), thus drivingthis drum and the shaft I I connected thereto.

Referring now to Fig. 3, it will be seen that each shoe I8 comprises ametal body 21 having an ars cuate convex cylindrical outer surface 28and two plane side surfaces 29 extending inwardly from the surface 28'.The plane surfaces 29 are approximately radial so that they converge inthe inward direction, and they are formed on two ribs 3| which extendinwardly at the opposite sides of the body 21. A sheet 32 of a suitablefriction material is secured in contact with the curved outer surface28, and a separate flat sheet 33 of a suitable friction material issecured in contact with each of the side surfaces 29. The shoes are soshaped with relation to the pockets that when a shoe is in its innermostposition, with the side sheets 33 on both sides engaging the flatsurfaces I9 of the adjacent ribs I5 (as shown in Fig. 2), there will bean appreciable clearance space between the curved outer sheet 32 and theinner surface of the surrounding drum 25. When a shoe is in itsoutermost position, with the curved outer sheet 32 in engagement withthe inner surface of the drum 25, and with one of the side sheets 33engaging the surface I9 of the adjacent rib I5 (as shown in Fig. 3)there will be an appreciable clearance space between the other sidesheet and the surface I9 of the adjacent rib.

Means is provided to hold the shoes I8 out of contact with thesurrounding drum 25 until they have attained a predetermined speed ofrevolution. For this purpose each shoe is provided with two pairs ofspaced ears 35 located at opposite sides of the shoe and extendinginwardly. Be-

tween the ears 35 of each pair there is mounted a cylindrical idlerroller -36 which is rotatably supported on a pin 31 extendingtransversely through the ears and parallel with the axis of the drum. Afiatk strip 39 of a suitable resilient material, such as spring steel,extends between the ears 35 of both pairs in a position outwardly of therollers 36, the ends of the strip engaging the adjacent inwardly facingshoulders I6 and the inner surface of the strip engaging the rollers.These parts are so arranged that when the shoes are in their innermostpositions the strips 39 will be substantially straight, whereas outwardmovement of the shoes will bend or deflect the strips outwardly into acurve, as shown in Fig. 3.

If the speed of rotation of the clutch greatly exceeds that necessary.to effect engagement of the shoes with the drum 25, the resultantcentrifugal force acting on the strips 39 will cause them to bend stillfurther outwardly. In case this outward bending is allowed to continue,the ends of the strip will be withdrawn from the retainingshoulders I6,and the strips will not return to their proper positions when the clutchis nally brought to rest. This difficulty is avoided in the presentinvention by providing a stop in the form of a U-shaped Vdevice 4Isuitably secured by welding or otherwise to the inner surface of theshoe body 21. This stop device 4I extends inwardly into proximity withthe outer .surface of the strip 39, with suillcient space be-v tweenthese parts to permit normal outward deflection of the strip and yetlimit this deflection f while the ends of the strip still remain incontact drum 25, at the same time flexing the springs 39,'

as shown in Fig. 3. The friction of the shoes against the inner surfaceof the drum will gradually accelerate the drum and the shaft I I untilall these parts are revolving at the same speed.

If the shaft IU is driven by an internal combustion engine or otherprime mover which produces a pulsating torque, the clutch will have adecided effect in smoothing out the pulsations, and the driven shaft I Iwill be substantially free from torsional vibrations. It will be notedfrom Fig. 3 that the torque is transmitted through the clutch by thepressure of the ribs I5 against one side of each shoe I8, the oppositeside of the shoe being spaced appreciably from the adjacent rib.Consequently there is permitted a limited relative motion between theribs I5 on the one hand and the drum 25 on the other hand, withoutrequiring any slipping of the shoes with relation to the drum. Duringsuch relative motion, the shoes move back and forth in a generallycircumferento the flat springs 39, and the rollers 36 will roll on thesprings and thereby prevent any appreciable friction which would tend toprevent such 5 motion. Thusthe angular velocity of the driving shaft I0may be alternately greater and less than that of the driven shaft II,and the angular velocity of the driven shaft will remain substantiallyuniform despite a pulsating torque in the driving shaft, so thattorsional vibration will be substantially eliminated from the drivenshaft. It will be understood that the torque pulsations may be eitherrapid or slow, depending upon the type of driving engine and itsconnection with the shaft I0, but ordinarily there will be at least oneor more pulsations for each revolution of the clutch.4

when the engine is of the internal combustion type.

As the speed rotation is increased, the centrifugal force acting on thesprings 39 will increase,

tending to flex these springs outwardly. At high speeds there is dangerof such flexing continuing so far thatthe ends of the springs will bewithdrawn from engagement with the inwardly facing shoulders I6, butthis is prevented by the action of the U-shaped devices 4I which liedirectly outside the springs and thus limit their outward movement.Consequently the springs will remain in position to withdraw the shoesI8 from contact with the drum 25 whenever the speed of rotation of thedriving shaft I0 is reduced to a predetermined value.

The fiat strips or springs 39 form simple beams of uniform cross-sectionfrom end to end, and

each beam is subjected to two concentrated loads oat predeterminedpoints.

deflections of such beams under given loads is a very simple matter, so'that the selection of the proper size of strip for a desired clutchengaging 40 speed is comparatively easy. The clutchcan thus be readilyadapted to various operating conditions. The construction is rugged anddependable, it will function asl an effective damper of torsionalvibrations, and it will operate satisfactorily throughout a long life ofuseful service despite the destructive effect of such vibrations.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A centrifugal clutch comprising two relatively rotatable coaxialmembers one of which provides a drum with an inner cylindrical surfaceand the other of which provides a series of circumferentially spacedabutments forming pockets therebetween surrounded by the drum, frictionshoes located in the pockets and so proportioned that when a shoe is incontact with the inner surface of thedrum and with one of the adjacentabutments a clearance will exist between the shoe Vand the otheradjacent abutment, a pair of spaced ears extending inwardly from eachshoe, a pin extending through the ears, an idler roller mounted on thepin between the ears, and a flat spring extending between the earswith.its inner surface engaging the roller and its ends supported by theadjacent abutments, the spring urging the shoe yieldably inwardly out ofcontact with the drum.

2. A centrifugal clutch comprising two relatively rotatable coaxialmembers one of which provides a drum with an inner cylindrical surfaceand the other of which provides a series of circumferentially spacedabutments forming pockets therebetween surrounded by the drum, frictionshoes located in the pockets and so propor- The calculation of thetioned that when a shoe is in contact with the innersurfaceof thedrumand with one of the adj acent abutments a clearance will exist betweenthe shoe and the other adjacent abutment, two pairs of spaced earsextending inwardly from each shoe, a separate pin extending through theears of each pair, an idler roller mounted on each pin between the ears,and a flat spring extending between the ears of each pair with its innersurface engaging both the rollers and its ends supported by the adjacentabutments, the spring urging the shoe yieldably inwardly out of contactwith the drum.

3. A centrifugal clutch comprising two relatively rotatable coaxialmembers one of which provides a drum with an inner cylindrical surfaceand the other of which provides a series of cirface and the other ofwhich provides. a series of circumferentially spaced abutments formingpockets therebetween surrounded by the drum,

cumferentially spaced abutments surrounded by the drum, friction shoeslocated between the abut- I ments and movable outwardly into engagementwith the inner surface of the drum under the influence of centrifugalforce, a flat spring located adjacent vthe inner side of each shoe withthe ends of the spring supported by the adjacent abutments, means oneach shoe engaging the inner surface of the adjacent spring at twopoints located on opposite sides of the center of the spring so that thespring will urge the shoe yieldably inwardly out of contact with thedrum, and means on each shoe in position to be engaged by the outersurface of the adjacent spring to limit outward deflection of the springunder the influence of centrifugal force.

provides a drum with an inner cylindrical sur' the abutments beingshaped to provide inwardly facing shoulders and approximately radialplane surfaces located outwardly of the shoulders, friction shoeslocated in the pockets, each shoe having an outer arcuate surface forcontact with the inner surface of the drum and two approximately radialplane side surfaces for contact with the said plane surfaces of theadjacent abutments, a ilat spring located adjacent the inner side ofeach shoe with its ends engaging the shoulders on the adjacentabutments, means on each shoe engaging the inner surface of the adjacentspring at two points located on opposite sides of the center of thespring so that the spring will urge the shoe yieldably inwardly out ofcontact with the drum. and a stop device extending inwardly from eachshoel into proximity with the outer surface of the spring at the centralportion thereoi to limit outward deection of the spring under theinfluence of centrifugal force.

LOUIS W. RAWSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

